Plasticity is clay’s ability to be shaped under pressure and hold its new shape without cracking or slumping. Highly plastic clays bend and stretch easily; short, less plastic clays crack and tear when you push them.
What Is Plasticity?
Plasticity comes from the tiny, flat shape of clay particles and the water held between them, which lets them slide over each other and then stay put. Fine-grained clays such as ball clay and bentonite are very plastic, while coarse clays, porcelains made mostly of kaolin, and bone china are short.
Throwing needs good plasticity, so walls can be pulled thin without tearing. Hand building and sculpture can work with less, especially with grog to add strength. Clay that is too plastic can be sticky and shrink a lot, so clay bodies balance plasticity with other properties.
Plasticity improves with ageing, as moisture spreads evenly through the clay, and with thorough wedging. Clay that has been worked too long on the wheel can become flabby and lose its strength, so many potters rest their clay or swap to a fresh piece.
A quick test is to roll a coil and bend it around your finger. Plastic clay bends smoothly, while short clay cracks on the outside of the curve.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.